Currently, various apparatuses using optical devices are used as ophthalmologic apparatuses. For example, an anterior ocular segment photographing apparatus, a fundus camera, and a confocal scanning laser ophthalmoscope (SLO) are used as optical devices for observing eyes. Thereamong, a tomographic imaging apparatus based on optical coherence tomography (hereinafter referred to as “OCT”) utilizing multiwavelength lightwave interference is an apparatus capable of obtaining a tomographic image of a sample at high resolution. The tomographic imaging apparatus is becoming indispensable for retina-specialized outpatient departments as ophthalmologic apparatuses.
The tomographic imaging apparatus splits low-coherence light from a light source into reference light and measurement light. Then, the tomographic imaging apparatus irradiates an inspection target with the measurement light and causes the reference light to interfere with return light from the inspection target. Thus, the tomographic imaging apparatus can measure a tomographic layer of the inspection target. The tomographic imaging apparatus can obtain a high-resolution tomographic image (hereinafter sometimes referred to as an “OCT tomographic image”) by scanning a sample with measurement light. Accordingly, tomographic images of a retina of a fundus of a subject's eye are acquired. Such tomographic images are widely used for ophthalmologic diagnoses. However, if the inspection target is a biological organ such as an eye, in order to suppress distortion of an image due to a motion of an eye, it is required to measure a tomographic layer at high speed with high sensitivity.
The United States Patent Application Publication No. 2008-0284981 discusses, as one of such methods, a method for simultaneously measuring data at a plurality of points on an inspection target. According to this method, light from a single light source is split by a slit so as to form a plurality of light sources. Then, each of light beams from the plurality of light sources is split by a beam splitter into a measurement light beam and a reference light beam. Each measurement light beam is applied onto an inspection target. A return light beam from the inspection target and the reference light beam are combined with each other by the beam splitter. Then, a plurality of combined light beams are incident upon a diffraction grating, and simultaneously detected by a two-dimensional sensor. Thus, the method discussed in the United States Patent Application Publication No. 2008-0284981 enables speed-up of the measurement by simultaneously measuring data using a plurality of measurement light beams.
However, when a single image is generated from images obtained by performing the measurement of data at a plurality of points on an inspection target, each connection part between the obtained images is noticeable according to a configuration of an optical system. More specifically, if interference light beams differ from each other in incidence angle to the diffraction grating, even when the incident light beams having the same wavelength width are incident thereupon, pixel widths detected on a sensor differ from one another due to characteristics of diffraction. Consequently, OCT images generated from the interference light beams differ from one another in contrast depending upon a depth direction of the inspection target, and in resolution.